1. Field of the Invention
The present invention, in a first aspect thereof, refers to a method for controlling a manufacturing process of components of a tyre for vehicle wheels. More specifically, the invention concerns a control method for detecting manufacturing defects in components of a tyre for vehicle wheels made through a process in which elongated elements fed by a dispensing member are distributed onto a forming support by means of at least one pressing member acting on such elongated elements along a pressing direction.
In a second aspect thereof, the present invention refers to an apparatus for the deposition of elongated elements in a manufacturing process of components of a tyre for vehicle wheels suitable for allowing the aforementioned method to be carried out.
2. Description of the Related Art
Throughout the present description and the subsequent claims, the term: elongated element is used to indicate an element in which the longitudinal dimensions are substantially greater than the transversal dimensions and the thickness, said element being made of an elastomeric material possibly comprising one or more thread-like reinforcing elements, such as fabric or metallic cords, incorporated therein.
It is also specified that, in the present description and in the subsequent claims, the term: elastomeric material is used to indicate a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such a composition also comprises additives such as, for example, a cross-linking agent and/or a plastifier. Thanks to the presence of the cross-linking agent, such a material can be cross-linked through heating, so as to form the finished product.
A tyre for vehicle wheels generally comprises a carcass structure comprising at least one carcass ply formed of reinforcing cords incorporated in an elastomeric matrix. The carcass ply has end flaps respectively engaged with annular anchoring structures, arranged in the areas usually identified with the name “beads” and each one normally formed of a substantially circumferential annular insert on which at least one filling insert is applied in a radially outer position.
In a radially outer position with respect to the carcass ply a belt structure is provided comprising one or more belt layers arranged radially one on top of the other and having textile or metallic reinforcing cords with crossed orientation and/or with an orientation substantially parallel to the direction of circumferential extension of the tyre. In a radially outer position a tread band, also made from elastomeric material like other structural components forming the tyre, is applied to the belt structure.
Between the tread band and the belt structure a so-called “underlayer” made of elastomeric material with suitable properties for ensuring a steady union of the tread band itself can be arranged.
On the side surfaces of the carcass structure respective sidewalls made of elastomeric material are also applied, each one extending from one of the side edges of the tread band up to the respective annular anchoring structure to the beads.
In tubeless tyres, the carcass ply is internally coated with a layer of a preferably butylene-based elastomeric material, usually known as a “liner”, having excellent characteristics of airtightness and extending from one bead to the other.
Conventional manufacturing processes of tyres for vehicle wheels essentially provide that the components of the tyre listed above are first of all made separately from each other and then are assembled in a subsequent tyre manufacturing step.
The current trend is, however, to employ manufacturing processes that allow the production and storage of semi-finished products to be minimised or, possibly, eliminated.
More specifically, attention has now turned towards process solutions that allow the individual components of the tyre to be made by directly applying them, according to a predetermined sequence, onto the tyre being manufactured on a preferably toroidal forming support.
In document WO 01/36185 to the same Applicant, the components of the tyre are formed on a toroidal support by sequentially applying onto the latter a plurality of elongated elements, consisting for example of individual rubberized cords or of rubberized cords grouped in parallel in the form of strip-like elements, particularly used for making the carcass and belt structure, and of continuous elongated elements made of elastomeric material, particularly used for making other structural components of the tyre, such as, for example, tread band, sidewalls, liner and filling inserts.
EP 0 968 814 A2 describes a process and an apparatus for distributing elastomeric materials for tyre-constitutional members. An elastomeric material for a tyre-constitutional member is laid down with high efficiency and high precision on a rotating support by arranging a pair of rollers rotating in opposite direction close to a radially outer surface portion of the support and using a gap defined between the rollers as a roller die.
It should be noted that in these cases the manufacturing of a tyre provides for an automated and substantially continuous process, i.e. substantially without intermediate storage of semi-finished products. In such a process the individual structural components of the tyre described above are manufactured according to a predetermined sequence starting from elongated elements fed by a dispensing member that can be operatively associated with an extruder and thereafter applied onto the forming support by means of at least one pressing member acting on the elongated element along a pressing direction.
A critical factor in continuous manufacturing processes of tyres of the type described above is the identification of anomalies that can intervene or occur during the manufacturing of one of the structural components of the tyre being formed due to an incorrect deposition of the elongated elements on the forming support. In fact, such anomalies cause imperfections or defects that may be hidden by a subsequently applied component and therefore no longer be detected directly on the finished tyre.
Most typical imperfections and/or defects encountered during the deposition step are those deriving from:                breaking of the elongated element with the consequent lack of deposition of the extruded material in the areas subjected to the dispensing cycle;        formation of discontinuities due to the presence of clots in the mix, or of brief mix portions with geometry not corresponding to that expected in output from the dispensing member (that can be caused by the presence of possible burnt portions or by operating anomalies of the dispensing member in operation);        formation of folds of material, particularly in the starting step of the deposition cycle.        
The Applicant has therefore felt the need to develop a method that allows the presence of possible defects or imperfections of deposition to be identified right from the deposition step of the aforementioned elongated elements on the forming support, in order to ensure ever higher quality levels in the tyres manufactured through continuous processes of the type described above.